This invention relates to jet drop copying systems of the general type disclosed in Paranjpe et al U.S. Pat. No. 4,112,469. In such systems an original document is positioned on a document support surface for scanning by an optical scanning system. An array of photosensing elements observes images of picture elements located at different positions within the picture frame being scanned and generates a series of control signals for switching control of a jet drop print head. The jet drop print head produces a line of spaced parallel printing jets, and directs these jets toward a print receiving medium mounted on a rotating drum. The drum is rotated in synchronism with the scanning of the original document under control of a control unit. Means are provided for giving the print head translational movement in a direction parallel to the axis of the rotating drum. The translational movement of the print head causes spiral interlacing of the printed tracks, so that solid printing coverage may be obtained.
The system taught by Paranjpe et al includes means for giving the optical system a translational motion corresponding to the motion of the print head, so that scanning and printing are carried out on a 1 for 1 basis. The photosensing elements accordingly have an arrangement corresponding to the arrangement of the orifices which produce the printing jets. Printing is conducted on a binary basis with each drop of printing liquid being directed either toward a catcher or toward a predetermined printing position.
Another prior art jet drop copier is disclosed in Fox et al, U.S. Pat. No. 4,051,538. Fox et al discloses a copying arrangement wherein a plurality of arrays of binarally switched jets cooperatively print an image upon a sheet mounted on a rotating drum. The printing jets are controlled by data stored within a memory.
Other prior art jet drop copying systems contemplate production of a printed copy during a single printing pass, as taught by Taylor et al, U.S. Pat. No. Re. 28219, or in King U.S. Pat. No. 3,739,395. Taylor et al contemplates a plurality of arrays of binarily switched jets, while King contemplates one or more arrays of electrostatically scanned jets. The King patent teaches binary deflection in a direction perpendicular to the direction of sideward scanning, with the binary deflection being operative to produce selective catching of drops not intended for printing.
Still another prior art ink jet copying system may use a print head of the general type disclosed in Paranjpe U.S. Pat. No. 4,122,458. In Paranjpe '458 the print head produces a row of jets which extend angularly with respect to a moving print web. Each jet is serviced by a series of vertically separated electrode elements, which are activated in sequence by a travelling voltage. The electrode elements provide deflection fields operative both for catching and scanning of drops.